Condenser bypass for two-phase electronics cooling system

ABSTRACT

An electronics cooling system utilizing a refrigerant fluid that evaporates to remove heat from electronics and is condensed back to liquid through heat exchange with a cold medium (air or water). The refrigerant fluid is circulated via a liquid pump between the condenser and heated evaporators. A bypass circuit is provided to divert flow around the condenser during conditions of cold ambient temperatures, which is controlled by a feedback loop using a mechanical or electronic control valve. This prevents the refrigerant fluid temperature from becoming very low and potentially inducing condensation on the outside of the refrigerant tubing from the warm and moist indoor air.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Patent Application Ser. No. 61/309,909, filed Mar. 3, 2010,the disclosure of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to an electronics cooling system utilizingan outdoor condenser and in particular to a valve controlled bypasscircuit is provided to divert flow around the condenser duringconditions of cold outdoor ambient temperatures.

BACKGROUND OF INVENTION

Power electronic devices, such as IGBTs, SCRs, etc., continue to achievehigher power switching capacity in a smaller envelope. The amount ofheat created by these devices continues to climb as well. Conventionalcooling methods include using blowing air, or circulating a water-basedfluid through cold plates in thermal contact with the electronic deviceheat sink. A more recent cooling method utilizes a phase change fluid,or refrigerant, that will evaporate to remove heat from an electronicdevice heat sink, and condense back to liquid state through heatexchange process with a cold medium (air or water).

FIG. 1 shows a diagram of a typical prior art two-phase pumped loopcooling system 110. Liquid refrigerant enters the pump 1, where staticpressure is raised and flow is induced. Sub-cooled liquid flows into anevaporator, shown herein as a plurality of cold plates 2, which can beconnected in series, or parallel, or both. The cold plates 2 are eachmounted in contact with the heat sink of the electronic device.Refrigerant fluid absorbs heat from the electronic device and partiallyevaporates as it flows through the cold plates 2. Partially evaporatedrefrigerant fluid is collected in a manifold, and then flows in thecondenser heat exchanger 4. The condenser heat exchanger 4 may be aircooled or water cooled and it may be located indoors or outdoors. Forthe condenser 4 to reject heat to a cold medium, the refrigerant fluidtemperature must be above that of the cold medium, or the ambient air.Since the refrigerant is undergoing a condensing process, therefrigerant pressure will follow the refrigerant temperature based onthe fluid's saturation pressure—temperature relationship. Therefrigerant fluid will leave the condenser 4 as a subcooled liquid, thetemperature will be above ambient, and the pressure will correspond toan even higher saturation temperature. The sub-cooled liquid flows intoa receiver tank 5, which acts a storage tank to compensate for varyingvolumes of the fluid in the system 110. The refrigerant fluid volume ofliquid and vapor will vary throughout the system 110 based on operatingtemperatures and heat load, due to varying densities through theoperating temperature range.

The system 210 shown in FIG. 2 is similar to that of FIG. 1, except thata liquid return line 6 is added from the cold plate exit manifold to thereceiver tank 5. The liquid return line 6 provides a pathway for liquidrefrigerant to return to the receiver tank 5, bypassing the condenser 4,while allowing the refrigerant vapor to proceed to the condenser 4. Inthis system 210 the liquid return line 6 is always open.

It is noted that in the prior art 2-phase cooling systems 110, 210, thesystem fluid pressure, and hence refrigerant fluid temperature willfollow the ambient air temperature at the condenser 4. The system fluidtemperature will be at some differential above the ambient airtemperature at the condenser 4. When the ambient air temperature at thecondenser is the same as the ambient air around the cold plates (such aswhere the power electronics devices and condenser are both locatedindoors), there will never be a danger of having moisture condensing outof the air and collecting on the fluid tubing, or pipes, or cold plates,and dripping onto the electronic devices, and damaging the electronicsbecause the fluid temperature will always be above the ambient air dewpoint.

A problem exists in these prior art systems when the power electronicsare located indoors (depicted in FIGS. 1 and 2 as area enclosed by adashed line and designated A), exposed to warm humid air, and thecondenser heat exchanger 4 is located outdoors (depicted in FIGS. 1 and2 as an area enclosed by a dashed line and designated B) and exposed toextreme cold temperatures. Since the refrigerant fluid temperature willclosely follow the condenser ambient air, there will be conditions wherethe refrigerant fluid entering back indoors will be cold enough to coolthe refrigerant fluid conduit surface temperature to a level below theindoor air dew point thereby causing condensation on the fluid conduitsand other system components from the moisture of the indoor air. Thismoisture can drip onto the electronic devices and cause damage fromshort circuiting.

SUMMARY

At least one embodiment of the invention provides a cooling systemcomprising: an evaporator, a pump, and a liquid receiver located in afirst environment having a first ambient temperature; a condenserlocated in a second environment having a second ambient temperature; arefrigerant fluid circulated through the system by the pump by a primaryfluid conduit to the evaporator, to the condensor, to the liquidreceiver, and back to the pump; and a valve adapted to selectivelyredirect fluid flow to bypass the condenser through a bypass fluidconduit located in the first environment.

At least one embodiment of the invention provides a cooling systemcomprising: an evaporator, a pump, and a liquid receiver located in afirst environment having a first ambient temperature; a condenserlocated in a second environment having a second ambient temperature; arefrigerant fluid circulated through the system by the pump by a primaryfluid conduit to the evaporator, to the condensor, to the liquidreceiver, and back to the pump; and a valve operable to redirect fluidflow from the evaporator to the liquid receiver through a bypass fluidconduit located in the first environment as needed in order to keep thefluid temperature within the first environment above a dew point of thefirst ambient temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this invention will now be described in further detailwith reference to the accompanying drawings, in which:

FIG. 1 is a schematic of a prior art cooling system;

FIG. 2 is a schematic of another prior art cooling system;

FIG. 3 is a schematic of an embodiment of the cooling system of thepresent invention utilizing a pressure control valve;

FIG. 4 is a schematic of another embodiment of the cooling system of thepresent invention utilizing a pressure control valve;

FIG. 5 is a schematic of still another embodiment of the cooling systemof the present invention utilizing a pressure control valve;

FIG. 6 is a schematic of another embodiment of the cooling system of thepresent invention utilizing an electronic control valve; and

FIG. 7 is a schematic of another embodiment of the cooling system of thepresent invention utilizing solenoid valves.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 3 shows a first embodiment of the cooling system of the presentinvention. The system 10 comprises an evaporator 2, a pump 1, and aliquid receiver 5 located in a first environment A having a firstambient temperature. The system 10 includes a condenser 4 located in asecond environment B having a second ambient temperature. A refrigerantfluid is circulated through the system 10 by the pump 1 by a primaryfluid conduit 21 to the evaporator 2, to the condensor 4, to the liquidreceiver 5, and back to the pump 1. The evaporator 2 is shown as aplurality of cold plates which can be mounted in the system 10 inseries, in parallel, or both. The cold plates of the evaporator 2 areeach mounted in thermal contact with the heat sink of an electronicdevice. Refrigerant fluid absorbs heat from the electronic device andpartially evaporates as it flows through the cold plates of theevaporator 2.

The system 10 also comprises a valve 3 operable to redirect fluid flowfrom the evaporator 2 to the liquid receiver 5 through a bypass fluidconduit 8 located in the first environment A as needed in order to keepthe fluid temperature within the first environment A above a dew pointof the first ambient temperature. The valve 3 as shown is a pressurecontrol valve 3. The partially evaporated refrigerant fluid leaving theevaporator 2 will enter the pressure control valve 3. The pressurecontrol valve 3 will divert refrigerant fluid to flow either to theoutdoor condenser 4 or to the bypass circuit 8, based on a pressurefeedback line 7 in comparison to a predetermined control valve internalset point. The pressure feedback line 7 is fluidly connected to theevaporator outlet line. The control valve 3 will divert flow to thecondenser 4 when the fluid pressure leaving the evaporator 2 is higherthan the internal set point. Otherwise, the control valve 3 will divertflow to the bypass circuit 8 and around the condenser 4 when the fluidpressure leaving the evaporator 2 is lower than the internal set point.The control valve internal set point will be set to a pressurecorresponding to a fluid saturation temperature that is above thehighest expected dew point for the indoor conditions. During operation,the refrigerant fluid will build up pressure based on the amount of heatentering the cold plate evaporators 2. If the system pressure is belowthe control valve set point, the refrigerant fluid will circulate intothe bypass circuit 8, and into the receiver tank 5, and back to the pump1. Thus, the refrigerant fluid will bypass the condenser 4 and not beexposed to extreme cold air temperatures. The refrigerant fluidtemperature will always be above the indoor air dew point, because it isnot exposed to any cold medium. With continued heat load on the coldplate evaporators 2, the refrigerant fluid temperature and pressure willexceed the control valve set point. With cold plate fluid pressureexceeding control valve set point, the control valve shuts off flow tothe bypass circuit 8 and allows flow to the condenser 4. Depending onthe heat load and outdoor ambient conditions, the system pressure maycontinue to rise (as in a warm outdoor temperature), or it may begin tofall again (as for a cold outdoor temperature). If the outdoortemperature is warm, the system pressure will settle at a steady-statepoint based on a temperature differential between the fluid saturationtemperature and ambient air temperature. This is a similar operation tothe prior art systems. If the outdoor temperature is extremely cold, thecontrol valve 3 will selectively allow flow to the condenser 4. As therefrigerant fluid is exposed to the very cold outdoor air temperature,the fluid temperature and system pressure will eventually drop. Thesystem pressure could drop below the control valve set point, andrefrigerant flow will again be diverted around the condenser 4 and intothe bypass circuit 8. Thus, the system self regulates, keeping the fluidpressure at or above the control valve internal set point. Therefore,refrigerant fluid temperature will always be above the indoor air dewpoint, due to the control valve regulating flow either to the outdoorcondenser 4 or around it. There will be no danger of having moisturecollect on the refrigerant tubing due to condensation, even with anoutdoor condenser 4.

FIG. 4 shows another embodiment of the system similar to that of FIG. 3except on where the bypass circuit is routed. In this embodiment thebypass circuit 8′ is routed directly into the top of the receiver tank5. Likewise the refrigerant fluid tube 9 leaving the condenser 4 is alsorouted directly into the top of the receiver tank 5. This embodiment ofthe invention allows liquid refrigerant that has accumulated in thecondenser to drain back into the receiver tank, thus providing moresub-cooling at the pump inlet.

FIG. 5 shows another embodiment of the invention. For this embodiment,the control valve 3 is placed between the condenser 4 and the receivertank 5. It accomplishes the same purpose in that it allows flow eitherfrom the condenser 4, or around it, based on fluid pressure leaving thecold plates 2. Fluid pressure leaving the cold plates 2 that is abovethe control valve internal set point will cause the control valve 3 toallow flow from the condenser 4 and shut-off the bypass circuit 8. Fluidpressure leaving the cold plates 2 below the control valve internal setpoint will cause the control valve 3 to block flow from the condenser 4and allow flow from the bypass circuit 8.

FIG. 6 shows another embodiment of a cooling system 10′″ of theinvention. The control valve 18 is in the same position as the systemdescribed in FIG. 3. However, for this system 10′″, the control valve 18is an electronic control valve. The cooling system 10′″ will have amicro-processor controller 12 that reads inputs from various sensors 11that monitor the refrigerant fluid temperatures and pressures andpossibly ambient air temperature. The micro-processor controller 12 willuse various fluid temperatures and pressures in an algorithm and willdetermine whether the control valve 18 should divert flow to thecondenser 4 or to the bypass circuit 8 around it. The micro-processorcontroller 12 will send an electronic signal to the control valve 18 toproperly position it.

FIG. 7 shows another embodiment of a cooling system 10″″ of theinvention. The control valve 10 could actually be split into two, 2-wayvalves 13, such as a solenoid valve; one valve 13A at the condenserinlet circuit, and one valve 13B on the bypass circuit as shown in FIG.7. The solenoid valves 13 are controlled by a micro-processor controller12, or could be simply wired in series to a pressure switch 11 locatedat the cold plate exit line. One solenoid valve 13 would benormally-closed, and the other solenoid valve 13 would be normally-open.High pressure at the cold plate exit line would activate the pressureswitch, which would close bypass circuit solenoid valve 13B, and openthe condenser entering line solenoid valve 13A.

Although the principles, embodiments and operation of the presentinvention have been described in detail herein, this is not to beconstrued as being limited to the particular illustrative formsdisclosed. They will thus become apparent to those skilled in the artthat various modifications of the embodiments herein can be made withoutdeparting from the spirit or scope of the invention.

1. A cooling system comprising: an evaporator, a pump, and a liquidreceiver located in a first environment having a first ambienttemperature; a condenser located in a second environment having a secondambient temperature; a refrigerant fluid circulated through the systemby the pump by a primary fluid conduit to the evaporator, to thecondensor, to the liquid receiver, and back to the pump; and a valveadapted to selectively redirect fluid flow to bypass the condenserthrough a bypass fluid conduit located in the first environment.
 2. Thecooling system of claim 1, wherein the valve is a pressure controlvalve.
 3. The cooling system of claim 2, wherein the pressure controlvalve has a predetermined pressure setpoint, the valve allowing fluidflow to the condenser when the pressure of the fluid entering the valveis greater than the pressure setpoint, the valve preventing fluid flowto the condenser and allowing fluid flow to bypass the condenser througha bypass fluid conduit located in the first environment when thepressure of the fluid entering the valve is less than the pressuresetpoint.
 4. The cooling system as in claim 1, wherein the valve islocated in the first environment downstream of the evaporator andupstream of the condenser.
 5. The cooling system as in claim 1, whereinthe valve is located in the first environment downstream of thecondenser and upstream of the liquid receiver.
 6. The cooling system asin claim 1, wherein the valve is an electronic control valve that isoperated by a micro-processor controller in response to at least one ofa pressure sensor or a temperature sensor.
 7. The cooling system as inclaim 1, wherein the bypass fluid conduit is connected to the primaryfluid conduit between the condenser and the liquid receiver.
 8. Thecooling system of claim as in claim 1, wherein the bypass fluid conduitis directly connected to the liquid receiver.
 9. A cooling systemcomprising: an evaporator, a pump, and a liquid receiver located in afirst environment having a first ambient temperature; a condenserlocated in a second environment having a second ambient temperature; arefrigerant fluid circulated through the system by the pump by a primaryfluid conduit to the evaporator, to the condensor, to the liquidreceiver, and back to the pump; and a valve operable to redirect fluidflow from the evaporator to the liquid receiver through a bypass fluidconduit located in the first environment as needed in order to keep thefluid temperature within the first environment above a dew point of thefirst ambient temperature.
 10. The cooling system of claim 9, whereinthe valve is a pressure control valve.
 11. The cooling system of claim10, wherein the pressure control valve has a predetermined pressuresetpoint, the valve allowing fluid flow to the condenser when thepressure of the fluid entering the valve is greater than the pressuresetpoint, the valve preventing fluid flow to the condenser and allowingfluid flow to bypass the condenser through the bypass fluid conduit whenthe pressure of the fluid entering the valve is less than the pressuresetpoint.
 12. The cooling system of claim 10, wherein the valve islocated in the first environment downstream of the evaporator andupstream of the condenser.
 13. The cooling system of claim 10, whereinthe valve is located in the first environment downstream of thecondenser and upstream of the liquid receiver.
 14. The cooling system asin claim 10, wherein the valve is an electronic control valve that isoperated by a micro-processor controller in response to at least one ofa pressure sensor or a temperature sensor.
 15. The cooling system as inclaim 10, wherein the bypass fluid conduit is connected to the primaryfluid conduit between the condenser and the liquid receiver.
 16. Thecooling system as in claim 10, wherein the bypass fluid conduit isdirectly connected to the liquid receiver.
 17. A cooling systemcomprising: an evaporator, a pump, and a liquid receiver located in afirst environment having a first ambient temperature; a condenserlocated in a second environment having a second ambient temperature; arefrigerant fluid circulated through the system by the pump by a primaryfluid conduit to the evaporator, to the condensor, to the liquidreceiver, and back to the pump; and a pressure control valve having apredetermined pressure setpoint, the valve allowing fluid flow to thecondenser when the pressure of the fluid entering the valve is greaterthan the pressure setpoint, the valve preventing fluid flow to thecondenser and allowing fluid flow to bypass the condenser through abypass fluid conduit located in the first environment when the pressureof the fluid entering the valve is less than the pressure setpoint. 18.The cooling system of claim 17, further comprising a pressure feedbackconduit.
 19. The cooling system as in claim 17, wherein the valve islocated in the first environment downstream of the evaporator andupstream of the condenser.
 20. The cooling system as in claim 17,wherein the valve is located in the first environment downstream of thecondenser and upstream of the liquid receiver.